This invention relates to a process for extracting sealed cartridges containing roasted and ground coffee, said cartridge being substantially in the form of a frustum or inverted frustum comprising an upper face and a lower face on which a filter is placed. The present invention also relates to a device for carrying out this process.
There are several reasons for the use of coffee capsules, above all in the field of espresso type coffees which are extracted under pressure, which include hygiene, optimal storage of the coffee, ease of use, better control of the quality of the coffee obtained and good reproducibility of the extraction conditions. Among the number of capsules available, only sealed capsules which open under the pressure of the water injected respond more completely to the reasons listed above. These capsules are distinguished by their opening system.
Some of these capsules are designed with weakened zones which tear preferentially under the effect of pressure. This solution has the disadvantage of increasing the complexity and price of the capsule because the materials used have to be treated very precisely to ensure that the capsules open correctly and reproducibly.
Other capsules are used in a process in which, in a first step, weakened zones are formed in the lower membrane by mechanical action; in a second step, these weakened zones tear under the pressure of the water injected so that the capsule is opened. A process of this type, which is described in French Patent 1 537 031 and French Patent Application Publication No. 2 033 190, has numerous disadvantages.
Firstly, it is difficult to carry out because the upper and lower faces of the cavity of the device intended to receive the capsule are provided with a number of projections and holes.
In addition, this process is neither reliable nor reproducible because it is impossible to obtain all the desired openings under the effect of the water pressure because, as soon as one or more openings has/have been obtained, the pressure falls in the capsule because the liquid is able to flow out.
Accordingly, the number and position of the openings are uncertain. This situation can give rise to poor extraction of the layer of the substance because, since the filter is placed against the lower face, it is not able to drain over its entire surface. Extraction is incomplete and heterogeneous (zones with preferential passages and poorly irrigated and drained zones).
In addition, a process of the type in question is unsatisfactory from the point of view of hygiene because, in view of the multitude of orifices for the passage of the water and the high temperature of the device, deposits of organic materials must inevitably occur.
Finally, the process in question may be sensitive to choking because the successive deposits of organic materials in the multitude of small orifices can contribute to their gradual obstruction. Under these conditions, the quality and uniformity of the extractions are affected to an even greater extent.
Finally, the process in question is used with capsules containing a powder-form or liquid starting substance. In the case of coffee, it can only be soluble coffee, which has to be dissolved with water, or a concentrated liquid coffee which has to be diluted with water.